If after having turned the E card we find an odd number on the back, we are lucky. We have found a card that has a vowel on one face and does not have an even number on the other - it has an odd number. This discovery proves that the rule is false and we can, therefore, stop here. However, if at the back of card E there is an even number, we have a confirmation of the rule. Now, though, we must turn over the 5 card and at the back of 5 card there may be a vowel. In this case the rule is false, because it does not have general validity. Even if at the back of the E card we find an even number, we now discover that there is a card with a vowel on the front and an odd number on the back.

If it is the first time we test ourselves with the Wason selection task and we have not answered correctly, we should not be surprised as the majority of people get it wrong. Since the Sixties, when Peter Wason, an English psychologist, pioneer in the study of human reasoning, created this test, it has been clear that only a few people answer correctly to this task, regardless of their level of education and their specialism. Initially, even professional logicians got the answer wrong. It must also be noted that not everyone who answers correctly has got there through the right reasoning. Sometimes they have just guessed the right answer.

Many people choose cards E and 2. This is wrong because, if we find an even number at the back of the E card, that is a confirmation of the rule,  we are stuck. In fact, if we turn over card 2 we may either get another proof that the rule is right or nothing relevant at all: if there is a vowel at the back of the card we have another confirmation of the rule but, if there is a consonant, the discovery will be irrelevant since the rule does not mention consonants. At the back of the 5 card, though, there could be a denial of the rule but we cannot turn any more cards.

Some choose to turn over the F card which doesn’t make sense if we have understood the rule. There are also some people who choose only one card and that, in this way, limit their options and prevent themselves from being able to solve the problem. Why does our mind make these mistakes? Sometimes a matching bias steps in: we seek only a match between what we say and what we do. The rule talks about vowels and even numbers and in the cards in front of us we have the vowel E and the even number 2. Thus, we turn cards E and 2 without thinking too much about it.

Sometimes we misunderstand the rule. The rule states that: If a card has a vowel written on the front, it will have an even number written on the back. It doesn’t say that the opposite is true: if a card has an even number written on the front, it will have a vowel on the back. We think and act as if the rule said both things that is known in logic as misunderstanding a conditional statement (if A…, then B…) for a double conditional statement (if A…, then B… and if B…, then A…). This misunderstanding of the rule can explain why sometimes we choose the 2 or the F cards. We want to verify whether at the back of the card with the even number there is or not a vowel or if at the back of the F card there is an even number. This would prove wrong our imaginary rule that at the back of the even number there is a vowel.

Often it is the confirmation bias that leads us to make a mistake. When we have a hypothesis in mind, in order to decide whether it is correct, we look for proofs that confirm our hypothesis instead of evidence that belie our hypothesis. In the Wason selection task, people choose E and 2 because are looking for proofs that confirm the validity of the rule. They don’t realize that it is more important to find proofs that reject the rule.

Errors in logic like those showed in the Wason test, like many others that nowadays we know about, are also made in medicine. For example, if we suspect that a patient has a given illness, we tend to look for proofs that confirm this and for other signs of this illness. From a logical point of view this is wrong. The best way to proceed is to look for counter-proofs. In fact, a denial of the rule is much more significant than a lot of confirmations that can be instantly disproved. Therefore, if we suspect that a person is affected by a given illness, the best strategy is to look for information that will allow us to exclude this hypothesis. Going on trying find proofs that confirm the suspect leads to an accumulation of information known as pseudo-diagnostic that is those information that allows the diagnosis to go on only on the surface which gives us the impression to know more and more without really contributing to finding a solution to the problem.

Research has shown that when doctors deal with clinical problems they generally tend to make less reasoning mistakes in comparison to the layman. Their reasoning skills are particularly good when they find themselves having to solve concrete problems in an area of expertise that they know well. In any case, even a doctor is subject to the common mistakes that the human mind tends to make. The mind of a doctor is that of a human being.

Why do we all make errors in our reasoning process? And why do doctors manage to reason better on medical questions and particularly on those that are familiar to them?

The situation is complex and research still has to clarify many things. However, what seems to be the main reason for this is that we have two kinds of minds: an adaptive mind and a rational mind. The former thinks in a way that helps us to deal with practical situations and especially in social contexts. The latter tries to understand how things really are and to evaluate things and make objective choices things. However, what seems to be the main reason for this is that we have two kinds of minds: an adaptive mind and a rational mind. The former thinks in a way that helps us to deal with practical situations and especially in social contexts. On the other hand, our rational mind tries to understand how things really are and to evaluate things and make objective choices.

Errors of reasoning are not mistakes for our  adaptive mind. On the contrary, these mistakes are useful for us to get by. For example, trying to look for confirmations and proofs of our idea does not help us to understand how things really are. However, it makes us feel good for the mere fact that it is more pleasant to gather information that proves our hypothesis right rather than denials. After all, my hypothesis is mine and, if it is confirmed, I get a confirmation of myself. Moreover, to deal with daily life, we do not always need to know exactly how things are. Often, it is enough to follow cautious rules that prevent us from encountering problems even if they are false.

When the situation requires from us to be objective, our adaptive mind must leave space for the rational mind. If this does not happen or does not happen enough, logical errors will not be functional anymore but will rather represent a problem for us.

There are some versions of the Wason selection task that help to understand how the two minds work. The one proposed at the bottom of the page is by Griggs and Cox. Here the answer is quite easy. Almost certainly we will choose the options ‘drinks beer’ and ‘is 16 years old’. Yet, if we think about it, it is as if we were choosing cards E and 5 in the Wason test. In this case, though, we are in a more concrete situation and we get to the solution with our adaptive mind, we do not need to be logical. However, our adaptive mind is essentially a social mind that is it works well in social  contexts and life situations. When as in the case of medical problems we are dealing with nature, we must use the rational mind, otherwise we run the risk of making mistakes. Probably, doctors have an advantage in doing this because clinical problems, especially those to which they are used to, form part of their life context.